Recently automobiles having an automatic speed change mechanism have run wild causing considerable damage, injuries and even death. Such wild running of automobiles can be attributed to the fact that, even if the driver does not press the accelerator, the rotational speed of the automobile engine is increased for no apparent reason. In automobiles in which automatic speed change mechanism are not provided, the driver presses the clutch at the time of starting the automobile, and the clutch is slowly and smoothly engaged. Therefore, even if the rotational speed of the engine is abnormally increased, the wild running of the automobile can be avoided because the driver can instantly detach the clutch. However, there is no clutch in an automatic transmission and, if the shift lever is switched from the neutral to the drive range, the automobile is accelerated correspondingly with the rotational speed of the engine. Therefore, if there is an abnormal increase of the rotational speed of the engine, a certain degree of wild running of the automobile cannot be avoided, at least for the time interval elapsing before the driver presses the brake.
Such a problem can be avoided if the driver presses the brake pedal when he shifts the shift lever from the neutral to the drive range. However, since the driver is a human being, it is difficult to observe such kind precautions, and therefore, the problem seems to remain as an unavoidable one. In this connection, in some automobiles, a mechanical device is installed which prevents the driver from shifting the shift lever from the neutral to the drive range without first pressing the brake pedal. By means of the above mentioned mechanical device, a sudden wild running of the automobile can be avoided, but in order to make it practical, a large number of mechanical components have to be arranged around the shift lever and the brake pedal. Furthermore, the related parts of the automobile have to be adapted to receive the new mechanical components, thereby increasing the manufacturing cost.